A study from the Center on Juvenile & Criminal Justice showed that marijuana decriminalization in California led to a significant drop in overall youth crime. The drop did not just come from the recategorization of misdemeanors related to marijuana, fewer crimes were committed after California decriminalized marijuana, effective the first day of 2011. Other drug felonies fell 36% and violent crime rates dropped 16% as well. Marijuana is not legal in California, but the penalties have been reduced over the years, and medical marijuana is legal in the Golden State.
The study goes much deeper, showing a steep drop off in crime when a 1976 California bill reduced marijuana possession from a felony to a misdemeanor. These crimes were still reported--so the numbers did not drop simply due to a recategorization--the law, along with socioeconomic factors, led to a sharp decrease in crime.
It does make sense after all. Much of the real damage done by marijuana revolves around establishing and protecting an illegal business. Reduce the criminal penalties around marijuana, and the rest of the criminal infrastructure decreases as well.
A debate is brewing over marijuana legalization in light of Colorado and Washington State voting for full legalization. California considered legalization in 2010, and Gov. Jerry Brown has called for the issue to be decided by the states instead of the federal government.